there are substrates based on dried and crushed corn.

but i wouldnt use food-based substrates, for environmental reasons and because i would worry about mold. i dont want to continuously throw away stuff that could be part of a fine meal for humans.

at shows its done for optics, you can get black, white, yellow, red or brown beans, also intricately patterned and striped beans. So at a show it gives you lots of possibilities to improve the optics. But in general, its just more expensive and more wasteful.